Vacuum packaging may be used to store perishables, such as foodstuffs. Storing perishable items in conditions that minimize exposure to oxygen and moisture may slow the degradation of these items during the time they are stored.
Various bags and tubing of plastic sheet material that may be formed into bags may be used for the purpose of vacuum sealing perishables. Tubing may be an extruded seamless tube, a folded sheet with a seam, two sheets joined with two seams, or other structure that provides a tube of plastic sheet material. Unsealed bags may be a length of tubing that is sealed with a seam at one end that is typically regarded as the bottom of the bag.
Commercial bags and tubing may consist of an inner layer of heat sealable thermoplastic and an outer layer of gas impermeable material. Additional layers may be used. The material may be uniform in thickness although each of layers may be of a different thickness than other layers. Such bags and tubing are generally inexpensive. Commercial bags may be troublesome to use. Commercial bags may not be evacuated effectively with home-type vacuum packaging machines that do not produce strong vacuums.
Home-type vacuum packaging machines may require the use of bags where the inner bag surface includes channels such as the bags described in U.S. Pat. No. 4,756,422. The channels in the home-type bags prevent the plastic sheets of the bag from clinging completely to the surface of the item being packaged. This may allow evacuation of the bag with a relatively weak suction. The channels may leave a residual volume that contains oxygen and moisture. Even if the bag is evacuated relatively well, the greater the residual volume, the greater the residual oxygen and moisture that the stored item is exposed to. It is desirable to minimize the residual volume when the bag is sealed. It may be particularly desirable to minimize the residual volume immediately adjacent to the stored item.
It would be desirable if commercial bags having smooth inner surfaces could be used with home-type vacuum packaging machines.